Centralized traffic controlling system for railroads



July 18, 1939. N. D. PRESTON 2,166,178

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Dec. 51, 1937 4 Sheets-Sheet 1 E (h 1 I O. HE Q w 1 A :1 o Y. n m. Q .4 't 'IH. F

. 2 Q, in u-a $3 Lq h 91 n "p D. lb S \JLL -|NVENTOR 4 Sheets- Sheet 2 N. Di PRESTON q -D Q Filed Dec. 51, 1957 July 18, 1939.

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July 18, 1939. N. D. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Dec. 51, 1937 4 Sheets-Sheet 5 a wm own! @4 m flluvllllul I .mw X E WN. mm- HM m;

July 18, 1939. D PRESTON 2,166,178

GENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Dec. 51, 1937 4 Sheets-Sheet 4 5 $9 4 L? TNvENToR Patented July 18, 1939 one STATES CENTRALHZED TRAFFIC CONTROLLING SYS- TEM FOR RAILROADS Neil B. Preston, Rochester, N. Y., assignor to General Railway Signal Company,

Rochester,

Application December 31, 1937, Serial No. 182,715

21 Claims.

This invention relates to a centralized traffic control system of the code type for governing the operation of track switches and signals on railstorage of switch and signal controls.

In the typical code communication system employed in a centralized tramc control system, code elements of variable character, such as positive or negative, short or long, and the like, are transmitted from the, control office to a field location during successive time intervals or steps; and the character of the code elements on such successive steps are employed to control the position of a track switch or switches, and the clearing of a signal for train movement in one direction or the other over the switch. It is usually desirable to transmit, on the same operating cycle of the systern, the control code for governing the position of the track switch and the clearing of av signal,

rather than control. the switch and check its response by waiting for a switch indication code before sending the signal clearing control code.

In the ordinary arrangement, to which the present invention more particularly relates, a suitable control device comprising a relay or relays is provided for each of the control steps, and distinctively conditioned in accordance with the character of the code element for that step. In such an organization, since the transmission of a given code element is only momentary, its control device is arranged to remain in "is last operated condition until subsequently changed; and. it may happen that a had contact, broken wire, or the like may prevent such subsequent change. in the existing condition of a control device in response to a code element subsequently transmitted, with the result that a switch or signal control code transmitted in accordance withthe wishes of the operator and. different from that previously stored, may not be properly registered and stored in the field.

The control apparatus and circuits for the switches and signals. in the field are ordinarily arranged in such a way that such a failure in the reception of a control code will not produce a dan erous condition in the sense of permitting collisionsbetween trains, or an unsafe operation of a switch or signal; but if a new control code is not properly received and stored at a field location, wrong route may be established, or a wrong signal cleared, or a signal already cleared put to stop, contrary to the intentions or wishes of the operator and in some instances affecting operation objectionably.

With these and other considerations in mind,

roads, and more particularly to the reception and and speaking generally and without attempting to define the nature or scope of the invention, it is proposed to provide suitable means for checking the response of the control device for each step to the character of the control code element transmitted for that step, and to discontinue automatically the reception of further control code elements as soon as any one of the control devices fails to respond properly. In other words, the reception of the control codes is checked step by step; and by thus checking response of the control devices for governing the position of a track switch on a step prior to the transmission of the signal clearing control code, the clearing of a signal for a wrong route is avoided. Further, bymaking the control for clearing or putting a signal to stop the last control that is received during the successive steps, then failure of the signal control device to respond to the character of the signal control code transmitted does not produce objectionable conditions materially affecting train operation in the sense that a signal is cleared or put to stop contrary to the intentions of the operator. In certain embodiments of the invention, provision is further made to check the response of the control means on the last step through the agency of a so-called execution circuit, so that the controlling condition for a signal is not changed unless the field apparatus takes the proper number of steps.

This invention is in the nature of a variation or improvement over the disclosure of the prior application of Wells, Ser. No. 145,070, filed May 27, 1937, and no claim is made herein to anything disclosed in that application.

Other characteristic features, attributes, and objects of the invention will be in part apparent and in part pointed out as the description progresses.

In the accompanying drawings, Figs. 1A and 213 when placed end to end illustrate in a simplified and diagrammatic manner one specific embodiment of the invention in a form suitable for governing the operation of a single switch and associated signals; Fig. 2 illustrates a variation or improvement in the arrangement of Figs. 1A and 1B by utilizing an execution circuit for rendering the signal clearing control on the last control step dependent upon the proper operation of the stepping relays; and Fig. 3 illustrates a modification employing neutral stick relays as switch and signal control devices, instead of the Magstick type of relay of Figs. 1A and 113.

For the purpose of simplifying the illustration and facilitating the explanation of the organization and mode of operation of the parts and circuits constituting this invention, the various relays and circuits have been shown diagrammatically with certain conventional illustrations. Thus, arrows with (-1-) and are used as symbols to indicate connections to the terminals of batteries or the like, instead of showing all of the wiring connections to these terminals.

The present invention is applicable, by suitable modification, for use with various types of code communication systems for centralized traffic control, and for various layouts of track switches and signals; and the particular organizations and arrangements illustrated in the accompanying drawings are merely typical or illustrative of specific embodiments of the invention and its application to one form of a code communication system for a typical single switch track layout.

The particular code communication system, to which the invention is illustrated as being applied in the accompanying drawings, is that type disclosed in the U. S. patent of Judge, et al., No. 2,082,544, dated June 1, 1937; and reference may be made to said patent for details of construction and operation of the code system not illustrated and described herein. For convenience, the various relays and other parts illustrated in the accompanying drawings which correspond to those shown in said patent have been given the same reference characters.

In this type of code communication system, a series of positive or negative current pulses are applied to a stepping and control line circuit to select a particular field station and to transmit to that field station the desired switch and signal controls. The number of impulses in the first part of the series for selecting a field station depends upon the number of field stations, and the number of impulses for a switch and signal control depends upon the number of switches. In the particular embodiment illustrated, three impulses are employed for station selection, and three impulses or steps for the control of a single switch and its associated signals. This is merely typical or illustrative; and the invention may be applied to any desired number of steps.

In the particular type of code communication system assumed, a station selecting stick relay S0 is employed for selecting the particular station to receive controls in accordance with the positive or negative character of the station code call transmitted. This station selecting relay S0 is initially energized at half of the stations in accordance with the positive or negative character of the initial energization of the line circuit during the conditioning period at the beginning of a cycle, and is maintained energized during each of the subsequent station selecting steps only at those stations whose code calls match the code being transmitted. This station selecting relay S0 at a station must be energized in order that controls may be received at that station, and also in the specific form shown for the operation of the stepping relays to continue.

In accordance with the principles and contemplated mode of operation of the present invention, a means is required to discontinue the reception of controls for any step upon failure of the control device for that step to respond properly to the character of the code element transmitted for that step; and one form of such a means is a stick relay controlled in the same manner as the station selecting relay SO. Accordingly, in the specific embodiment of the invention illustrated, the means for controlling the relay SO as disclosed in the above mentioned patent of Judge et al., for performing a station selecting function is supplemented by another means enabling this same relay to perform the function of checking the response of the switch and signal control devices step by step. In other words, the station selecting relay S0 is arranged to perform, in addition to its function of station selection, the function of checking the proper response of the switch and signal control devices. It should be understood, however, that this is merely one embodiment of the invention, and that a stick relay or equivalent means, entirely separate from the station selecting equipment may be employed for step-by-step check of the response of the switch and signal control devices in accordance with this invention.

Code system.-Before describing in detail the construction and mode of operation of the devices and circuits constituting the present invention, it is expedient to outline briefly the features of construction and operation of the code communication system with which the invention is used.

The control codes for governing the track switch and associated signals originate in the control office and are transmitted during an operating cycle to a selected field station over two line wires constituting a stepping and control line circuit. The control office equipment is not material to the present invention and has been illustrated conventionally at C0. The line wires are designated [0 and I2.

Each control code includes a certain number of code elements (three as shown) which constitute the code call for a particular station to which switch and signal controls are to be sent, and the remaining code elements (three as shown) have their character selected to provide for operating the track switch to the normal or the reverse position, to select whether the signal shall clear for train movement over the switch in one direction or the other, and to determine whether the selected signal shall be controlled to indicate clear or stop. In connection with this invention, it is desirable for reasons explained later to transmit the code elements for governing the position of the switch, direction of trafiic, and signal control in the order named.

The way in which different station code calls are set up in the control office by the operation of the starting buttons associated with the different stations, and the manner in which the character of the code elements for the switch and signal control are determined by the position of the switch and signal control levers are illustrated and explained more in detail in the Judge et al., Patent No. 2,082,544 above mentioned; and for the purpose of explaining and understanding the present invention, it is sufficient to point out and appreciate that, when the switch and signal levers belonging to a particular control station in the field have been positioned by the operator, and the starting button for such station has been actuated, the control office equipment is set into operation for an operating cycle during which the code call for the desired station is transmitted to pick out that station, and the appropriate controls for governing the switch and signals are received and stored at that station.

Referring to Fig. 1A, the station equipment for receiving the control cod-es comprises a three-p0- sition polar line relay F included in the stepping and control line circuit, and having its armature biased to a neutral position. When the system is at rest, this line relay F is de-energized and its contacts ItI and H4 are in the de-energized or middle position as shown on the drawings. This line relay F is energized with one polarity or the other for each code element of the control code, and assumes its de-energized position during the chi period of de-energization between the successive code elements. This line relay F operates a neutral repeater relay FF and governs the operation of a slow release cycle marking relay SA and its repeater SB.

The field station apparatus also includes a bank of stepping relays IV, 2V, 3V, etc. five being shown. These stepping relays are energized sequentially one at a time for each step by the dropping of the relay FP during the off periods between the energizations of the line circuit for the successive code elements. The circuits for operating these relays of the stepping bank are illustrated and explained more in detail in the patent to Judge, et al above mentioned, and in various other patents, such as Preston, No. 2,084,466, dated June 1, 1937. For the present purposes, it is suificient to note that when the line circuit is tie-energized after its initial conditioning energization, the first step relay IV is picked up and stuck until the end of the operating cycle, and the other step relays 2V, 3V, etc. are similarly picked up and stuck one at a time in turn during successive off periods or de-energizations of the line circuit. There is a step relay for each code element; and the number of step relays required depends upon the number of stations to be selected and the number of controls to be transmitted to each station.

The field station equipment also includes a station selecting stick relay SO and associated relay for station selection purposes. A particular combination of and impulses or code elements, conveniently termed a station code call, is allotted to each station of the system; and at each station code jumpers, such as III, H2, and M3 in Fig. 1A, are arranged differently at these different stations in conformity with their respective code calls. The code call for the station illustrated in Fig. 1A is assumed to be In the particular arrangement shown, the polarity of the initial energization of the line circuit during the conditioning period for an operating cycle is employed as the first code element of the station selecting code call.

The present invention in the specific form illustrated employs a station selecting relay SO as part of the means for checking the response of the switch and signal control devices to their respective code elements; and it is expedient to consider at this point the control circuits and operation of the relay SO in some detail.

Assuming that a control cycle is initiated in the control ofiice to call the station shown in Fig. 1, the first energization of the line circuit will be positive and the contact IM on the line relay F is consequently moved to the right, thereby establishing a pick-up circuit through the upper windings of the relays SO and SOS in series which may be traced from back contact I08 of relay polar contact H t of line relay F to the right, back contacts I5, I6, H5, H6 and II? of the step relays 5V, 4V, etc., code jumper II I, and upper windings of relays SO and SOS to The energization of relay SO closes its front contact H8 to maintain this relay energized so long as the line relay F remains in its operated position and irrespective of the energization of the relay SA.

A station selecting relay S0 is similarly energized at all of the other stations which have a code call with positive for the first code element. At such other stations, as well as at the station of Fig. 1A, this initial energization of the line relay F closes an energizing circuit for the relay FP through a back contact I82 of the relay SB, and also through the front contact I ID of relay SO when that relay becomes energized. The closing of the front contact I01 of relay FP energizes the relay SA, which in turn closes its front contact 183 and energizes relay SB. The onergization of relay and the closing of its front contact i'rlfi establishes a stick circuit for relay SOS through the front contact I23 of relay FF and front contact I24 of relay SOS; and with relay SOS energized, a stick circuit for relay S0 is also established through a front contact I22 of relay SB, front contact I25 of relay SOS, and front contact I26 and lower winding of relay SO.

At other stations whose code call does not match the positive impulse assumed to be transmitted, the code jumper I I I is in a different position, and relays SO andSOS are not picked up. Relays SA and SB are energized at these stations, but when relay SB picks up and opens its back contact IE2, relay FP drops, SA continuing to receive current through the back contact H0 of relay S0. The relay FP at these other stations remains down during the remainder of the cycle, and there is no stepping operation or reception of controls at these stations.

Following the initial energization of the line circuit for the conditioning period, the control ofli'ce equipment opens the line circuit, relays F and F? drop, and the first step relay IV is picked up. As soon as the polar contact H4 of the line relay F moves from its operated position, the energizing circuit through the upper windings of relays SO and SOS is broken; but relay SOS is held up by its stick circuit, in turn holding up relay SO by its stick circuit, until relay FP opens its front contact I23. As soon as relay FP closes its back contact I23, a stick circuit through the lower winding of relay S0 is established to hold up this relay, but relay SOS drops. The relay S0 is preferably constructed to release quickly, as for example during the movement of the polar contact I Hi of the line relay F from one position to the other, as might occur under exceptional circumstances where the positive or negative code element is muti ated by a line surge; and for'this reason the relay SOS is provided to hold up the relay SO during the time from the opening of the po ar contact of relay F until relay FP makes its back contact I23.

During the next energization of the line circuit after the first step relay IV picks up, this energization assumed to be positive, an energizing circuit through the upper windings of relays SO and SOS is established through the front contact lid of relay SO, polar contact H4 of line relay F to the right, back contacts I5, I6, I I5 and H6 of the stepping relays 5V, 4V, 3V, and 2V, front contact I ll of step relay IV (now energized) code jumper H2, through the upper windings of the relays SO and SOS. This circuit holds up relay SO and picks up relay SOS, and establishes at the station of Fig. 1A and at all other stations which may have a positive code element for the second step, the same condition as existed after the conditioning period above explained. At other stations this energizing circuit for the upper windings of relay SO and SOS is not establishechand relay SO drops when relay FP picks up and breaks at its back contact I23 the stick circuit through the lower winding of relay S0. The dropping of relay S0 at these stations opens the front contact I [8, so that the relay SO cannot thereafter be energized on any subsequent step during that operating cycle.

This same general plan of operation is repeated for the next code element of the station selecting code call, assumed to be for the station of Fig. 1A and may be repeated for as many steps as desired until, at the completion of the station selecting code elements, a relay S0 is energized at only one station. At all the other stations the relay SO either fails to pick up at all, or is de-energized during the transmission of some other code element; and at all of these stations the line relay repeater FF is de-energized, and no further operation of the stepping bank occurs. Also, the energizing circuits for the switch and signal control devices include the front contact H8 of the relay SO, as will appear later, so that with this relay SO de-energized no controls can he received. In other words, when a field station relay SO drops out during the station selecting part of the cycle, the stepping operation ceases at that station and reception of controls is prevented.

Checking the response of the control devices.- Considering now the apparatus and circuits more particularly characterizing the present invention, in order to facilitate an explanation and understanding of the nature of the invention, it has been illustrated as applied to the control of a single track switch and its associated signals by three control devices; but it should be understood that the invention may be applied to any desired number of switches, signals, or other devices to be controlled.

In the simple arrangement assumed, one of the control devices WR governs the position of the track switch, another device DR selects or de termines the direction of train movement over the switch, and a third device GR controls the stop or clear indication of the signal selected by the position of switch and direction of train movement chosen. These switch and signal control devices are preferably arranged to be operated on successive steps in this same order.

In the embodiment of the invention illustrated in Figs. 1A and 1B, the control devices or relays WR, DR, and GR are assumed to be of the type, commonly known as a mag-stick relay, which is constructed as disclosed, for example, in the patent to W. D. Hailes et al., No. 1,929,094, October 3, 1933. This type of mag-stick relay is provided with a permanent magnet and two windings; and when one winding is energized (the lower winding as illustrated) the armature of the relay is attracted to close a front contact and is held in that position by the permanent magnet after the flow of current through said winding ceases, and until the other winding is energized to overcome the attraction of the permanent magnet and cause the armature to assume its retracted position and close back contacts. This particular construction of relay is merely illustrative of the type contemplated by this invention in which a movable element is operated to different positions by the energization of two windings, and is maintained in the last operated position until subsequently changed.

Various organizations and arrangements of control circuits for governing the power operated switch machine and the associated signals by such control devices WR, DR, and GR may be employed with various expedients in the Way of switch locking and the like; and since the particular scheme of such application circuits performs no part of the present invention and may consist of any arrangement suitable for the purpose, a simplified organization of switch and signal control circuits has been illustrated, without attempting to incorporate the various features of switch locking and the like that would be employed in practice. One typical arrangement of application circuits in a more complete form, is disclosed, for example, in the prior application of De Long, Ser. No. 98,611, filed August 29, 1936.

In the simplified arrangement of switch and signal interlocking circuits shown in Fig. 1B, the switch machine SM for operating the switch W is assumed to be operated to the normal or re verse position in accordance with the polarity of the energization of the control circuit including contacts 29 operated by the switch control relay WR, contacts 2i of a suitable lock relay L being included in this circuit for preventing operation of the switch under certain conditions. It is assumed that, when relay WR is operated to attract its armature into the position shown, the switch machine is operated to the normal position, subject to such suitable approach, detector or route locking as may be desired and employed to control the lock relay L.

The position and locked condition of the switch W is manifested by the energized condition 01' a neutral-polar switch repeating relay WP, in the manner well known in the art; and a contact 22 on the switch control relay WR co-operates with the contacts 23 and 2A of the switch repeater relay WP toenergize normal and reverse correspondence relays NCR and RCR when the switch points have been operated and locked in the normal or the reverse position in correspondence with switch control relay WR.

The circuits for clearing the respective signals iA, IB, 2A, and 2B, governing train movement over the switch, are controlled by the contacts 2528 of these correspondence relays NOR and RCR, so that no signal can be cleared until the switch is over and locked in a corresponding position. It is assumed that these signals will also be controlled by track circuits in a suitable manner, as indicated by the contacts EH and 21-1. The control relay DR selects by its contact 28 whether the signal IA or EB for an east-bound train movement from left to right shall clear, or signal 2A or 2B for a west-bound train movement; and the control relay GR controls by its contact 30 the clear or stop indication of the signal selected by the control relay DR and 130-- sition of the track switch, the selected signal being cleared if relay GR is energized and being put to stop if this relay is dc-energized.

OpCTGtiOiL-RGfEIlillg to the embodiment of the invention illustrated in Figs. 1A and 13, assume as a typical example that the operator olesires to set the switch W to the reverse position from the normal position shown and to clear the signal lB for an east-bound train, it having been assumed in this connection that the last operated condition of the control relays WR and DR was for the normal position of the switch a west-bound train movement.

After the station selecting operation already described has occurred, and step relay V3 picks up for the first control step, the polar contact. H4 of the line relay F is operated tothe left to establish an energizing circuit for the upper winding of relay WR which may be traced from all) (-1-) through front contact H8 of relay SO, polar contact M4 to the left, back contacts ll and [8 of step relays 5V and 6V, front contact H9 of step relay 3V, wire 35, through the upper winding of relay WR, and back contact 3% of relay GR to Such energization of, the upper winding of the relay WR is assumed to cause the armature 3'! of this relay to be retracted, as indicated by the arrow; and if this relay properly responds, current is conducted through its back contact 3'5, wire 38 through front contact 39 of relay 3V, back contacts 49 and M of relays 4V and 5V, back contact 42 of a relay LV, wire 43, to the upper windings of relays S0 and SOS, thereby holding up relay SO and preventing its deenergization when relay FP picks up and breaks its stick circuit.

It will be noted that this sustaining circuit for the relay SO includes in effect the polar contact I Hi of the line relay Fin a corresponding position with the contact 3? of the control relay WR, so that if this control relay fails to assume a condition in correspondence with the code element being transmitted, the sustaining circuit for relay S0 is not energized, and it is released when relay PP picks up to break its stick circuit.

Control relay WR receives current by operation of the polar contact of the line relay at the same time as theline repeater relay FF; and unless the control relay WR is slower in its operation than the relay FP, current is supplied to the upper winding of relay SO before its stick circuit through its lowerwinding is broken at the back contact E23 of relay FP. Relay SO,

however, is preferably made somewhat slow releasing by including its lower winding in a closed circuit through a resistance 34 and a front contact 45 of the step relay 3V.

After the switch control element has been transmitted and received, the next relay W is operated, and then the code element for the selection of the direction of traffic is applied to the line circuit. If, as assumed, this code element is of a negative character to release the armature of relay DR, the polar contact Ht of relay F is operated to the left, and a. circuit similar to the one just traced is established through the upper winding of relay DR and back contact 69 of relay GR. If the relay DR properly responds to this control and releases its armature, current is supplied through its back contact ll, wire 48, through the front contact 46 of step relay -V and back contacts M and 42 of relays 5V and LV, to the upper windings of relays SO and SOS,

in substantially the same Way as previously explained.

On the last step, with step relay 5V energized, the signal control relay GR is similarly controlled.

The release of the armature of relay WR shifts its contacts 28 to cause operation of the switch machine SM to the reverse position; and when the switch points assume the reverse position and change position of-polar contact 24 of relay WP, the reverse correspondence relay RCR is energized. With back contact 29 of the trafiic direction control relay DR closed, and front contact 30 of signal clearing relay GR closed, the

clearing circuit for signal IB, readily traced on the drawings, is closed and energized to clear the desired signal. These operations are typical and well known, and need not be further discussed. On the sixth deenergization of the line circuit the last stepping relay LV is energized through the following circuit: beginning at the terminal front contact I33 of relay SB, front contact !34 of relay SO, back contact I35 of relay FP, back contact M!) of relay VP and front contact 53 of stepping relay 5V. This energization of the last stepping relay LV deenergizes the relay SO and signifies the end of the control cycle.

As shown, the signal control relay GR governed on the last control step is illustrated as being provided with a contact 5E? and Wire 5! to maintain energization of the relay SO, although there is no subsequent controls to be transmitted. This is to assure that the relay SO will be maintained energized on the last control step, more particularly for the purpose of providing a suitable execution circuit for use in the modification of Fig. 2.

From this explanation it can be seen that if control code is transmitted to change the position of the switch control relay WR, and if a bad contact, broken wire, or the like, prevents the energization of a winding of the relay to change it from its existing position, then the relay S0 is released, because the position of the contacts of the control relay WR fails to match the position of the polar contacts of the line relay F. Such deenergization of the relay SO not only prevents the operation of the control relays for any subsequent steps, due to the opening of the front contact H8, but also prevents further operation of the relay FF and further stepping operation. The same is true for traffic direction controlling relay DR.

Consequently, if the control for the switch as transmitted is not properly received by the response of the relay WR, there is no further stepping or reception of controls, and hence no clearing of the signal for a wrong route. Similarly, if the control for the direction of traffic is not properlyreceived, the signal clearing relay GR is not controlled, and no signal is cleared for the wrong direction.

The energizing circuits for the switch control relay WR and trafiic direction controlling relay DR includes back contacts 36 and 49 of the relay GR, so that if this relay GR is energized to clear a signal, the relays WR and GR cannot be changed by any subsequent code, and their failure to respond to a control code different from the existing condition stops the stepping and receptionof controls. This prevents any change in the position of the switch or direction of traffic established when a signal has been controlled to indicate clear, so that no clear signal may be improperly put to stop.

A signal which has been cleared is automatically put to stop by a train dropping the track relay T of the detector section to close its back contact 58 and apply current through the front contact 52 of the slow release repeater relay TP, to the upper winding of the relay GR and operate its armature to the released position. A signal that has been cleared by mistake or prematurely may be put to stop by the operator by transmitting a control code for the same position control is transmitted. The failure of the signalcontrol relay GR to respond to a clear or stop control transmitted, however, does not create objectionable conditions in the sense of producing an operationcontrary to the intentions of the operator. The signal control relay GR, after having been once conditioned to either clear a signal or put it to stop, tends to remain in that condition until subsequently changed by the proper reception of a control code calling for such change. For example, if the relay GR is in the stop position shown, it will remain in that condition until a signal clearing code is transmitted and properly received; and failure of this relay GR to respond to a control code, due to a bad contact, broken wire or the like, means that the operator will not be able to accomplish what he desired, but will not create a situation contrary to his Wishes, such as clear a signal for the wrong position of the switch or for the wrong direction of traffic.

From the foregoing it can be seen that this invention provides an arrangement for checking the response of the control devices step by step, and for discontinuing further stepping and transmission of controls if a control device on any step fails to respond properly to the character of the code element being transmitted. By arranging for controlling the position of the switch and the direction of traffic on steps prior to the control of the signals to indicate clear, it is assured that no signal can be cleared for the wrong position of the switch or for the wrong direction.

Modification Fig. 2.In special and exceptional circumstances the stepping relays at a field station may take an extra or extraneous step at some point in an operating cycle, so that the code elements as transmitted from the control office for certain steps are received on different steps in the field station. To take care of such contingency of a garbled code, it is proposed to employ the modified arrangement shown in Fig. 2, in which an execution circuit is employed to govern the operation of a neutral stick relay GRP repeating the condition of the signal control relay GR of Fig. 13, said execution circuit being closed to permit a change in the relay GRP only if the field apparatus has taken the proper number of steps. In other words, if the field station should for any reason take an extra or false step, the execution circuit is not closed at the end of the cycle, and the relay GRP governing the signals is not disturbed from its existing condition.

In this arrangement, when the line circuit is deenergized after transmission of the last code element, a relay LV picks up in the same manner as if it were an extra step relay as shown and described in the patent to Judge et al., No. 2,082,-

544 above mentioned; and the relay SO, if still energized, is maintained energized by its stick circuit upon dropping of the relay FP during this de-energization of the line circuit in the same way as for other steps. The control ofiice keeps the line circuit open at the end of the cycle long enough to allow the slow release relays SA and SB of the system to drop, release the stepping relays and otherwise restore all the apparatus to the normal condition ready for another operating cycle. If the stepping bank at the field location has taken the proper number of steps, the energization of the relay LV occurs at the end of the cycle, and when the slow-release relay SA drops, an execution circuit is completed through its back contact 55, a front contact 56 of relay SO, and a front contact 57 of the relay LV. If, however, the stepping bank at the field station has for some reason taken an extra step, the relay LV is energized prior to the end of the cycle and there is a subsequent energization of the line circuit by the control office, which picks up the relay FF and releases the relay SO, the sustaining circuit for the relay SO through its upper winding being broken at the back contact 42 of the relay LV. Consequently, when the control office opens the line circuit for the end of the cycle and the relay SA drops, the execution circuit is not con plete, because relay SO has been in the meantime released.

Assuming that a signal clearing code is trans-- mitted to pick up the relay GR, if this relay GR properly responds, the relay S0 is maintained energized; and if the proper number of steps are taken, the execution circuit is closed to energize the upper winding of the relay GRP through the front contact 66 of relay GR. The relay GRP is stuck up by a stick circuit from through the front contact 6| of the detector track relay T, through the front contact 62 of the relay GR in multiple with the back contact 63 of the execution relay EX, front contact (i l of relay GRP through its lower winding to When a train enters the detector track circuit this stick circuit for the relay GRP is broken to put the signal to stop and cancel the signal clearing code. A back contact 65 of a slow-release repeater track relay T? is provided in multiple with the front contact 6| of the detector track relay T, so that a stick circuit for the signal clear ing relay GRP is established with a train on the detector track section, thereby enabling a signal clearing code to be received and stored with a train present. This is optional.

If the operator wishes to put a signal to stop which has been cleared prematurely or by mistake, a control code for the same switch position and direction of trafiic is transmitted with a stop code element of that polarity on the last step. If the relay GR properly responds, and if the proper number of steps are taken, the stick circuit for the signal controlling relay GRP is broken when the execution relay EX picks up and opens the back contact 63, front contact 62 of relay GR being open at this time under these conditions.

The relay EX is preferably stuck up through its lower winding, front contact 68, wire ill, and back contact 55 of relay SA, until the beginning of a subsequent cycle, so that there will be ample time for relay GRP to release.

From this explanation it can be seen that the modification of Fig. 2 provides, in addition to the step-by-step check of Figs. 1A and 13, a further check against an over-step condition, and prevents the reception of a signal control code in the case of an extraneous extra step. In this connection, it should be noted that when the relay GRP is energized to clear a signal, the opening of its back contacts l8, l9 prevent operation of the switch control relay WR and traffic direction controlling relay DR by any control code. Once the relay GRP has been energized to clear a signal, it cannot be de-energized by a control code except during a normal and a proper cycle; and it is thus assured that no route established can be changed by an improper operation of the code communication system, or a signal falsely put to stop in the face of a train contrary to the wishes of the operator. When the relay GRP is de-energized, the relays WR and DR may be changed during an incomplete or over-step cycle; but since the relay GRP will not be energized to clear a signal under such conditions, there will be merelyan idle operation of the switch machine and an ineffective selection of direction of trafiic. The operation of the switch machine, of course, cannot occur if there is a train on the detector track circuit.

Modification of Fig. 3.--There is illustrated in Fig. 3 a variation or modification similar to that of Figs. 1A and 1B in which neutral stick relays are employed to receive and store the switch and signal controls instead of mag-stick relays. The switch is controlled by two neutral relays WN and WP; the direction of traffic is selected by a similar pair of relays RG and LG; and the clear-and stop indications of the selected signal are governed by the clearing control relay GCL and stop relay GSTP respectively.

Considering the switch control relays WN and WR, the energizing circuit for the upper winding of the relay WN is energized by a positive impulse on the line circuit, and is connected through its front contact ill to a maintaining circuit for the relays SO and SOS, in a similar manner and for the same purpose as the contact iii of the magstick relay WR of Fig. 113. If the relay WN fails to pick up and close its front contact in, in'response to a corresponding code element, the relay S0 is de-energized. The relay WN has a stick circuit including its lower winding, its front contact a i, and a back contact l2 of the other relay WR; and the relay WN once energized is maintained energized by this stick circuit until the other relay WR is energized. The other relay WR is provided with similar control circuits; and the two relays WN and WR control the operation, of the switch machine.

The relays GR and GL selecting the direction of train movement are similarly organized; and the signal control relays GCL and GSTP are likewise provided with pick-up circuits and contacts for maintaining the relay SO energized. The stick circuit for the signal clearing relay GCL, however, includes in addition to a back contact 13 of the stop relay GSTP, a front contact M of the detector track relay T, thereby enabling the signal clearing code to be automatically cancelled by a train entering the detector track circuit. The stick circuit for the stop relay GSTP includes a front contact 75 of the relay GCL, so that this relay is maintained energized by its stick circuit only temporarily until the signal clearing relay GCL releases.

The operation of this modification of Fig. 3 is substantially the same as that already described for Figs. 1A and 1B, and need not be further explained.

The various organizations and arrangements of parts and circuits illustrated and described are merely typical or representative embodiments of the invention; and various changes may be made in the specific structures illustrated without departing from the underlying principles and characteristic features of the invention.

What I claim is:

1. In a centralized trafiic controlling system for railroads, field equipment for receiving control codes consisting of time spaced code elements each variable in character comprising, step-bystep means operating to a new step position for each code element irrespective of its character, a plurality of control devices each rendered responsive in turn by the operation of said step by-step means to the distinctive character of the corresponding code elements, and means included wholly within said field equipment effective upon any step of said step-by-step means for preventing further operation ofsaid step-by-step means whenever a control device for that step fails to assume a condition in conformity with the code element transmitted for that step, whereby failure of any control device to respond properly to its code element stops further operation of the stepby-step means and prevents the reception of any subsequently transmitted controls.

2. In a centralized trafiic control system for governing the operation of track switches and associated signals, field apparatus for receiving and storing switch and signal control codes each comprising a plurality of time spaced code elements each variable in character comprising, a code following relay assuming different conditions in accordance with the character of the cede elements, a bank of stepping relays governed by said code following relay and assuming a new step position for each code element irrespective of its character, a plurality of control devices each rendered responsive in a predetermined order to the distinctive character of the succes" sive code elements by the operation of said bank of stepping relays, a stick relay operating if in the deenergized position to prevent further operation of said stepping bank, means for temporarily energizing said stick relay prior to the transmission of a control code, and means for maintaining said stick relay energized only so long as the control device for each step in turn assumes a condition in conformity with the operation of said code following relay on the co=rresponding step, whereby failure of a control device on any step to respond properly to the code element being transmitted causes deenergizatio-n of said stick relay to stop further operation of the bank of stepping relays and prevent operation of the control devices for any subsequent steps.

3. In a centralized traflic control system for governing the position of a power operated track switch and the indications of signals adapted to govern train movement in either direction over said switch in either position, field equipment comprising a plurality of control devices, one of said control devices governing the position of said track switch, a traffic direction control device selecting the direction of train movement, a signal control device governing the clear and stop indications of the signal for the position of the switch and direction of traffic determined by the other control devices, means including step-- by-step apparatus for rendering said controi vices responsive one at a time in turn and in the order named to the character of the successive code elements transmitted, and means included wholly within said field equipment effective when ever any one of said control devices fails assume a condition corresponding with the character of the code element being transmitted on a particular step of said step-by-step means for preventing operation of the control devices for any subsequent steps, whereby the control device governing the clearing of the signal cannot be operated in response to the reception of its control code element unless the control devices for the position of the switch and direction of traffic have both properly responded to their respective code elements.

4. Field apparatus for centralized traffic control systems for receiving and storing the character of successive switch and signal control code elements comprising, a code following relay assuming distinctive conditions in accordance with the character of the successive code elements as transmitted, a bank of stepping relays-governed till by said code following relay to take a step for each code element irrespective of its character, a plurality of control devices each adapted to assume distinctive conditions in accordance with the distinctive character of a corresponding code element and to remain in such condition until subsequently changed, a power operated track switch and associated signals, one of said control devices governing the position of said switch, another of said control devices governing the indication of said signals, means including said bank of stepping relays for rendering said control devices responsive in the order named to the operation of said code following relay by the successive switch and signal control elements being transmitted, a stick relay acting if deenergized to stop further operation of said bank of stepping relays, means for temporarily picking up said stick relay prior to the operation of said stepping bank for said control steps, a stick circuit for maintaining said stick relay energized during the operation of said stepping bank for each of said control steps, and means including cooperating contacts of said control devices and contacts operated by said code following relay for opening said stick circuit on any step if the control device for that step fails to assume a condition in conformity with the operation of said code following relay by the character of the code element then being transmitted.

5. In a centralized traffic control system for railroads, field apparatus for receiving and storing the distinctive character of a plurality of code elements of a control code comprising, a plurality of control devices one for each code element and each including two windings and having contacts distinctively operated by the energization of said windings, control means including step-by-step apparatus for energizing one or the other winding of each of said control devices in turn on the successive steps in accordance with the charact r of the successive code elements being transmitted, and means wholly included within said field apparatus effective during the transmission of any one of said code elements whenever the contacts of the corresponding control device fail to assume a position corresponding with the character of such code element for preventing the energization of the windings of the control devices to be controlled on any subsequent steps by rendering said control means ineffective and stopping only the operation of the step-by-step apparatus of said field apparatus, whereby the response of the control devices to their respective code elements is checked step-by-step and the reception of code elements is automatically discontinued whenever a control device fails to respond properly.

6. In a code communication system of the character described, field apparatus for receiving and storing the distinctive character of a plurality of code elements of a control code comprising, a plurality of pairs of neutral control relays one pair for each code element of a control code, energizing circuits for said relays, line relay means operating contacts to distinctive positions for the different characters of each code element, means including step-by-step apparatus for connecting the energizing circuits of each pair of said control relays to the contacts of said line relay means one pair only for each of the successive code elements, and means wholly included within said field apparatus responsive to the correspondence in the position of the contacts of the line relay means on a particular step of said step-by-step means and the contacts of said control relays controlled on that step to prevent operation of the control relays to be operated on any subsequent steps Whenever the control relays for a step fail to assume conditions in conformity with the character of the code element being transmitted on that step.

'7. In a centralized traffic control system for governing the position of a power operated track switch and the indications of signals governing train movement over said switch, field equipment for receiving and storing switch and signal control codes consisting of successive code elements of variable character, said field equipment comprising, a plurality of pairs of neutral control relays including a normal neutral control relay and a reverse neutral control for respectively governing the operation of the track switch to the normal and reverse positions, a signals right neutral control relay and a signals left neutral control relay for respectively governing opposite directions of traflic, a signal clear neutral control relay and a signal stop neutral control relay for respectively governing the clear and stop indications of the signals, step-by-step means operating to take a step for each code element transmitted irrespective of its character, energizing circuits for said switch control relays and for said signal control relays respectively established in succession in the different positions of said stepby-step apparatus, a chucking relay having a contact included in all of said energizing circuits, and means for operating said checking relays to open its contact on any step whenever the control relays for that step fail to be energized in accordance with the character of the corresponding code element being transmitted.

8. In a centralized trafiic control system for governing the position of a power-operated track switch and the indication of the associated signals governing train movement over said switch in both directions, field equipment for receiving and storing switch and signal control codes comprising, a control device for governing the position of the track switch, a second control device for determining the direction of train movement over the switch, a third control device for governing the clear and stop indications of the selected signal, each of said control devices operating contacts to different positions for code elements of difierent polarity in which positions they remain until again operated, a polar line relay closing contacts in different positions in accordance with the polarity of the successive code elements, means including step-by-step' means and energizing circuits for rendering said control devices responsive one at a time and in the order named to the condition of said line relay as operated by the successive code elements being transmitted, and checking means operable to break all of said energizing circuits for said control devices on any step whenever the control device for that step fails to operate its contacts to a position corresponding with the position of the contacts of said line relay, whereby failure of any control device to respond properly to the code element being transmitted prevents the operation of the control device for any subsequent steps.

9. In a centralized trafiic control system for transmitting switch and signal control codes to any selected one of a plurality of field stations, field apparatus for each station for rendering the apparatus at that station only responsive to control codes and for receiving and storing such control codes, said field apparatus comprising, a

bank of stepping relays operating to take astep for each code element of the station selecting code call and of the control code, a-plurality of control devices one for each element of the control code, a station selecting relay which must be energized to permit operation of said control devices, an energizing circuit for said relay, means for closing said energizing circuit temporarily at the beginning of an operating cycle, means including code jumpers and contacts of certain relays of said bank of stepping relays for maintaining said selecting relay energized during the transmission of the successive code elements of a station selecting code call only if such code elements then being transmitted correspond with said code jumpers, and means including contacts operated by said control devices and contacts of other relays of said bank of stepping relays for maintaining said selecting relay energized during the transmission of successive code elements of a control code only if each of said control devices in turn operates its contacts to a position in conformity with the character of the corresponding code element being transmitted, whereby failure of a control device on any step to respond properly to the character of its code element causes deenergization of the same relay employed for station selection and stops reception of further control code elements.

10. In a centralized traffic controlling system for governing the operation of a track switch and the indications of the associated signals at a number of field locations, code receiving and storing equipment at each field location comprising, line relay means operating contacts to different positions in accordance with the character of the successive code elements of a station selecting code call and of a switch and signal control code, a bank of stepping relays operated by said line relay means to take a new step position for each of said code elements irrespective ofits character, a station selecting stick relay, means for temporarily energizing said station selecting relay at the beginning of the operation of said bank of stepping relays, code jumpers arranged distinctively in accordance with the code call for the particular station, stick circuit means governed by said bank of stepping relays for maintaining said station selecting relay energized during the transmission of the successive station selecting code elements only if the position assumed by the contacts of said line relay means on each of the successive steps for said station selecting code call corresponds with the arrangement of said jumpers, a plurality of control devices one for each code element of the control code for governing the position of the track switch and the indications of the associated signals, means governed by said bank of stepping relays for rendering said control devices responsive one at a time in turn to the position assumed by the contacts of said line relay means but only if said station selecting relay is energized, each of said control devices having contact means operated to a different condition dependent upon the'character of its governing code element, said stick circuit means for said station selecting relay being governed by the contacts of said control devices and the contacts of said line relay means to maintain said station selecting relay energized during the transmission of the successive control code elements only if each of said control devices in turn operates its respective contact meansto a condi tion corresponding with the existing position of the contacts of said line relay-means, whereby failure of a control device on any step to respond properly to the control code element being transmitted causes de-energization of the station selecting relay and prevents control of the control devices on any subsequent steps.

11. In a code communication system of the character described for governing the operation of track switches and signals at a number of different field locations, field equipment for each field location comprising, a polar line relay operating contacts to different positions in accordance with the polarity of the successive code elements of a station selecting code call and a switch and signal control code, a bank of stepping relays operated in response to the successive energizations of said line relay to take one step for each code element irrespective of its polarity, code jumpers arranged in a distinctive manner in accordance with a station selecting code call allotted to the particular station, a station selecting stick relay, means for temporarily energizing said selecting relay at the beginning of an operating cycle of said bank of stepping relays, a pair of neutral control relays for each control step, means including contacts of certain relays of said bank for energizing one or the other relay of each pair on the successive control steps dependent upon the polarity of energization of said line relay on such steps and only if said station selecting relay is then energized, stick circuit means for maintaining the station selecting relay energized only if the code jumpers for the station matches the position assumed by the contacts of said line relay on the successive steps of the transmission of the station selecting code call, and also only if the control relay of the pair for each step closes a contact to match the energized condition of said line relay for that control step, whereby said station selecting relay is de-energized on any step to discontinue reception of control codes at the corresponding station whenever the code jumpers at that station fail to match the station selecting code call being transmitted and also whenever the control-relays for any control step fail to respond properly to the polarity of energization of said line relay for that step.

12. Code receiving and storing apparatus for centralized traflic control systems for railroads comprising, a polar line relay responsive to the polarity of successive code elements of a control code, a bank of stepping relays governed by said line relay to take a new step position for each code element irrespective of its polarity, a pair of control relays for each control step, an energizing circuit for each control relay including acontact of a corresponding step relay and a polar contact of said line relay, a checking relay having a front contact included in the energizing circuits for all of said control relays, and an en ergizing circuit for said checking relay including a plurality of multiple branches, each of said branches including a contact of a step relay and contacts in multiple of the control relays for that step connected to the respective energizing clrcuits for that control relay, whereby said checking relay is de-energized during the transmission of any one of said code elements to discontinue reception of further control codes whenever the proper control relay on any step fails to become energized and close a contact to correspond with the position of the polar contact of said line relay on that step.

13. Code receiving and storing apparatus for code communication systems comprising, line relay means-responsive to the distinctive character of the successive code elements of a control code, a bank of stepping relays governed by said line relay means and energized one at a time sequentially for each code element irrespective of its character, a plurality of control devices one for each of said code elements, each of said control devices having two windings and contact means operated to different positions by the energization of the respective windings, an energizing circuit for each winding of each control device including a front contact of a corresponding step relay and a contact of said line relay means closed for a particular character of code element, a checking stick relay having a front contact included in said energizing circuits for all of said control relays, means for temporarily energizing said stick relay prior to said control steps, and a stick circuit for said checking relay including its own front contact and a plurality of branches in multiple established in succession by the operation of said stepping relays, each of said branches being closed only if the contact means of the corresponding control relay is operated to a position to conform with the condition of the contacts of said line relay means, whereby said checking relay is de-energized on any step to prevent operation of the control devices on any subsequent steps whenever a control device fails to operate its contact means in accordance with the condition to which said line relay means is operated by the character of the code element being transmitted.

14. In a system of the character described for governing the position of a power-operated track switch and the indications of associated signals, a switch control relay for governing the operation of the switch to the normal or the reverse position, a traflic direction control relay for selecting the direction of train movement over the switch, a signal control relay for governing the clear and stop indications of the signal for the position of the switch and direction of traffic determined by the other control relays, each of said control relays having contacts magnetically held in the last operated position after de-energization of the relay until subsequently changed, code receiving means including a bank of stepping relays for rendering said control relays responsive one at a time in turn and in the order named to the character of the successive code elements, and means included wholly within said code receiving means efiective during operation of any one of said stepping relays whenever the control relay controlled on that step fails to assume a condition in accordance with the character of the code element being transmitted on that step for preventing operation of the control devices to be controlled on subsequent steps by the code elements transmitted on such subsequent steps, whereby the control relay for governing the indications of the signal cannot be operated from its existing condition unless the control relays for the position of the switch and direction of traffic have both properly responded to their respective code elements during the same operating cycle.

in a system of the character described for governing the position of a power-operated track switch and the indications of the associated signals, line relay means responding distinctively to the character of the successive code elements of a station selecting code call and a switch and signal control code, a plurality of pairs of pen-- tral control relays, one pair governing the position of the switch, another pair selecting the direction of traflic over this switch, and another pair governing the clear and stop indications of a signal, step-by-step means operated to a new step position for each code element irrespective of its character for rendering said pairs of control relays responsive in turn and in the order named to the condition of said line relay means, a station selecting relay acting only if energized to permit said pairs of control relays to be governed by the operation of the line relay means, means for initially energizing said station selecting relay at the beginning of an operating cycle of said step-by-step means, a stick circuit for said station selecting relay, means for closing said stick circuit during the station selecting steps,

only if the code call allotted to the station matches the character of the code elements of the station selecting code call being transmitted, and means for closing said stick circuit during each of the steps of said switch and signal control code only if one or the other of the pair of control relays for that step is energized to conform with the character of the corresponding code element being transmitted, whereby said station selecting relay is de-energized on any step to prevent the reception of subsequent controls whenever the code call allotted to that station fails to match the station selecting code call being transmitted and also whenever the control relays for any step fail to respond properly to the character of the corresponding code elements of the switch and signal control code.

16. In a code communication system for governing the indications of wayside signals, the combination with a wayside signal and an adjacent track circuit, a signal control relay for governing the clear and stop indications of said signals and having two windings, said control relay having contacts operated to one position upon energization of one winding and remaining in that position after de-energization of that winding until the other winding is subsequently energized, a polar line relay responsive to the polar character of the code elements of a control code, a bankof stepping relays energized sequentially one at, a time by the operation of said line relay for each code element irrespective of its character, means governed by a particular one of said stepping relays for rendering the energization of one winding or the other of said signal control relay dependent upon the character of the code element for that step, whereby said signal control relay may be governed to cause said signal to indicate clear or stop, and means governed by said track circuit for only momentarily energizing said other winding of said signal control relay upon the entrance of a train into said track circuit for causing said signal to indicate stop.

17. Code receiving and storing apparatus of the character described for control codes consisting of time spaced code elements each variable in character comprising, a line relay energized and de-energized for each code element, a slow-release cycle marking relay governed by said line relay and maintained energized during the repeated operations of said line relay by the transmission of a control code, a bank of stepping relays energized sequentially one at a time by the operation of said line relay for each code element irrespective of its character, an extra step relay energized by the operation of said line relay at the end of an operating cycle, a plurality of control relays successively rendered responsive to the successive code elements by said stepping relays, said control relays being positioned on each step in accordancewith the character of the code element for'that step as repeatedby said line relay, a plurality of devices, a stick relay having one stick circuit including a back contact of said extra step relay and another stick circuit including a contact controlled by the operation of said line relay, said stick relay being tie-energized by the operation of said line relay after the extra step relay is energized, and an execution circuit including a back contact of the slow-release cycle marking relay, a front contact of said stick relay, and a front contact of said extra step relay, said execution circuit acting to render said control relays effective to govern the operation of said device, whereby said execution circuit is not closed unless the bank of stepping relays operates to take the proper number of steps in conformity with the operations of the line relay and said devices are not controlled by said control relays until the end of an operating cycle.

18. In a code communication system for centralized traffic control, apparatus for checking the response of control devices to a predetermined number of successive code elements of variable character transmitted during a series of steps of the same number comprising, in combination with a line relay, a slow-release cycle marking relay governed by said line relay and maintained energized during the operation of that line relay by successive code elements, said cycle marking relay assuming its de-energized condition at the end of an operating cycle, a bank of stepping relays energized sequentially one at a time in response to the operation of said line relay during the transmission of the successive code elements, a plurality of control devices successively rendered responsive to the successive code elements by said stepping relays, said devices being for the control of traflic governing devices, an execution relay for rendering certain of said control devices effective to control their traffic governing devices at the end of an operating cycle, means for energizing said execution relay at the end of an operating cycle of said bank of stepping relays only if the number of stepping relays energized corresponds with said predetermined number of code elements, and a stick circuit for said execution relay including a back contact of said cycle marking relay, whereby the execution relay after being energized at the end of a normal cycle is maintained energized until a succeeding operating cycle.

19. In a code communication system for centralized traffic control for railroads, the combination with a wayside signal, of code receiving apparatus for governing the clearing of said signal comprising, a line relay responsive to the character of the successive code elements of a control code, a particular one of said code elements having one character or another for clearing or putting to stop said signal, a slow-release cycle marking relay maintained energized during an operating cycle of transmission of the control code and assuming its de-energized condition at the end of such operating cycle, a bank of stepping relays energized sequentially one at a time for each code element, an execution relay, an execution circuit for energizing said execution relay at the end of an operating cycle upon de-ener ization of said cycle marking relay only if the operation of said bank of stepping relays corresponds with the number of code elements received, a stick circuit for said execution relay maintained energized while said cycle marking relay is de-energized, a signal control relay conditioned in accordance with the character of said particular code element and maintained in such condition only until the end of the corresponding operating cycle, a signal clearing relay having a pick-up circuit energized from said execution circuit only if said signal control relay is then energized, and a stick circuit for said signal clearing relay including in multiple a front contact of said signal control relay and a back'contact of said execution relay.

20. In a system of the character described for governing the power operation of a railroad track switch and the clear and stop indications of signals for governing traflic in opposite directions over said track switch; line relay means responsiveto the distinctive characters of the successive code elements of a control code; a bank of stepping relays governed by said line relay means, said stepping relays being energized sequentially one for each code element irrespective of its character to comprise a cycle of operation; a

switch control relay for governing the power operation of the track switch to the normal or reverse position, a traffic direction control relay for selecting the direction of train movement over the track switch, a signal control relay for governing the clear and stop indications of the signals, each of said control relays being of the polarized magnetic stick type in which its contacts are magnetically held in the last operated position until a subsequent energization of the relay; circuit means controlled by said stepping relays and effective to render said control relays responsive one at a time each on a step of said stepping relays and in, the order named to the character of the successive code elements, each of said control relays being energized on its step in accordance with the character of the code element then repeated by said line relay means, said circuit means allowing the energization of said switch control and said direction control relays only if said signal control relay is positioned for causing all of said signals to indicate stop; and circuit means wholly included within said code receiving apparatus effective during each step, if the control relay for that step fails to take a position in accordance with the character of the code element for that step, for preventing the energization of the control relay for any subsequent step or steps of the cycle of operation, if any; whereby the signal control relay for governing the indications of the signals cannot be operated from its existing condition unless the control relays for governing the position of the switch and the direction of traffic have both properly responded to their respective code elements during the same operating cycle of said step-by-step means.

21. In a centralized traific controlling system for railroads of the character described; a power operated track switch with associated signals and a detector track section; line relay means responsive to the distinctive characters of the successive code elements of a control code; a bank of stepping relays governed by said line relay means and energized one at a time sequentially in response to the code elements of said control code; a switch control relay for governing the power operation of the track switch to the normal or reverse position, a traflic direction control relay for selecting the direction of train movement over the track switch, a signal control relay for governing the clear and stop indications of the signals, each of said control relays being of the polarized magnetic stick type in which its contacts are magnetically held in the last operated position until a subsequent energization of the relay; circuit means controlled by said stepping relays and efiective to render said control relays responsive one at a time in turn in the order named to the character of the successive code elements, each of said control relays being energized on its step in accordance with the character of the code element then repeated by said line relay means, said circuit means allowing the en ergization of said switch control and said direction control relays only if said signal control relay is positioned for causing all of said signals to indicate stop; circuit means efiective dining each step, if the control relay for that step fails to take a position in accordance with the character of the code element for that step, for preventing the energization of the control relay for any subsequent step or steps if any; a track relay controlled by traffic in said detector track section; a track repeating relay directly controlled by said track relay; and circuit means rendered eifective upon the deenergization of said track relay and controlled by said track repeating relay so as to energize said signal control relay only momentarily in a manner to actuate its contacts to positions which require said signals to indicate stop, whereby said signal control relay can be subsequently energized to opposite positions by a control code although a train still occupies said detector track section.

NEIL D. PRESTON. 

